Physical coloring, also referred to as coloration using particle scattering, provides many benefits relative to previous coloration approaches such as dyes and pigments. The previous approaches suffer problems with fading, recyclability, toxicity and other environmental concerns. Moreover, physical coloring enables many new properties, such as switchability from one color state to another due to light exposure, temperature changes, or humidity changes. Various compositions that achieve physical coloring are discussed in commonly-assigned U.S. Pat. No. 5,932,309, entitled “Colored Articles And Compositions And Methods For Their Fabrication”, issued Aug. 3, 1999, and incorporated herein by reference.
In particular, physical coloration can provide switchability from one color state to another. Such color changing compositions can be used, for example, for cosmetic purposes in polymer fibers used for textiles and carpets, and for color-changing windows and displays. Additionally, this type of technology could be used in military applications for camouflage clothing, tents, and machinery. If such color change is reversibly switched as a consequence of light exposure, temperature changes, or humidity changes, then chameleon effects can be achieved for such articles. If the color switching effect is a one-time event caused by actinic radiation or high temperature exposure, the switching effect can be used to provide spatially dependent coloration. Enhancing the value of polymer films, fibers, coatings, and other articles by achieving novel optical effects provides a major commercial goal.
In the prior art, U.S. Pat. No. 4,886,687 describes non-pigmented coloration as a result of diffraction effects originating from an embossed pattern having 5,000 to 100,000 lines per inch. U.S. Pat. No. 4,017,318 describes glass articles that, after exposure to actinic radiations, can be heat treated to provide coloration effects because of colloidal silver particles. U.S. Pat. Nos. 2,515,936; 2,515,943 and 2,651,145 also describe methods of generating colored silicate glasses using combinations of various colloidal metals, including colloidal gold and silver. Pearlescent compositions, such as described in U.S. Pat. Nos. 3,087,829 and 4,146,403, provide coloration due to the interference of light reflected from parallel opposite sides of platelets deposited on the plate sides of mica substrate particles. U.S. Pat. No. 3,586,417 shows that the wavelength at which a Christiansen filter transmits can be varied for an optical device by varying the temperature of the filter. Such variation results from the different temperature coefficients for the refractive indices of the scattering particles and the liquid matrix. Various new methods for producing Christiansen filters, including some efforts to make solid-matrix optical devices, are described by Balasubramanian, Applied Optics 31, pp. 1574-1587 (1992).
However, the prior technologies do not provide the advantages of using coloration associated with particle scattering, or materials and methods for modifying and enhancing the coloration effects of particle scattering. Moreover, the prior technologies do not provide inks and other coatings that are based on physical color technology, and which can be controlled based on their electrical, magnetic, and/or photo properties. The present invention addresses these and other issues.